Field of the Invention
The present invention relates to a high frequency heating apparatus, and more particularly, to a high frequency heating apparatus which heats a substrate by applying high frequency waves thereto.
Description of Related Art
The use of glass materials in a variety of industrial fields, specifically, as a cover for a photovoltaic cell, a flat display such as a thin-film transistor liquid crystal display (TFT-LCD), a plasma display panel (PDP) or an organic electroluminescent (EL) device, a variety of mobile electronic devices, and the like, is rapidly increasing. Accordingly, glass materials are required to have lightweight and a thin profile.
However, the trend in glass materials towards a light and thin profile leads to a problem of fragility due to its high brittleness. Accordingly, a variety of tempering methods is being studied in order to improve the durability of glass.
Glass tempering technologies of the related art include chemical strengthening technology that uses an ion exchange between the glass surface and a water solution (molten salt) and thermal strengthening technology that includes heat treatment on glass.
The chemical strengthening technology has the drawbacks of poor usability regarding process time necessary for the ion exchange between the glass surface and a water solution, the size of the glass, recycling of the water solution (contamination and concentration control), and the like.
In contrast, the thermal strengthening technology strengthens glass by increasing the temperature of a plate glass and quenching it while moving the plate glass in a hot horizontal furnace. A variety of methods for applying this technology in the industry are underway since heating using high frequency waves has an advantage in that the heat treatment effects are enhanced due to volume heating and rapid heating is enabled.
However, in the case of heat-treating a plate glass having a large size by applying the high frequency technology of the related art, the use of a single high frequency generator is disadvantageous in that control over electric field distribution inside a chamber is difficult and the temperature growth rate is low. Although the use of a plurality of high frequency generators increases the temperature growth rate to a certain degree, concentration in electric fields due to interference between the high frequency generators leads to localized heating in the glass and the decreased heating efficiency, which is problematic.
FIG. 1A and FIG. 1B are pictures of electric field distribution analysis and temperature distribution analysis of a plate glass that are measured after heat-treating the plate glass using a high frequency heating apparatus having a plurality of high frequency generators of the related art. In FIG. 1A, the apricot area represents the portion where no electric field is formed. In FIG. 1B, the blue area represents a low temperature, and the red area represents a high temperature. It can be appreciated that the corner areas of the heat-treated plate glass are not heated since no electric fields are formed in these areas. In addition, hot spots are formed in localized areas of the plate glass due to the interference of the electric fields.
Accordingly, in the case of high frequency heating using a single high frequency generator, the problem is that the temperature growth rate is low. In the case of high frequency heating using a plurality of high frequency generators, the problems are that localized heating occurs due to the interference between high frequency waves generated by the high frequency generators and the concentration in electric field although the temperature growth rate is improved to a certain degree.
The information disclosed in the Background of the Invention section is only for the enhancement of understanding of the background of the invention, and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.